Same problem here, resolved by
http://www.shadowbox-js.com/doc/forum.html
search for
Start ShadowBox with Slideshow Paused
or
http://n2.nabble.com/Start-ShadowBox-wi ... l#a1310919
As other have noted setting it to 0 makes the play button vanish.
Also setting the delay param to 0 did not work for me, debugging shows it's being passed a value of 7 !!!
components/com_phocagallery/views/category/view.html.php line 244, could not figure out why because
$sb_slideshow_delay = $params->get( 'sb_slideshow_delay', 0 ); should be 0.